Mbed-OS platform overview
The Mbed-OS platform is a Matter platform that uses Arm Mbed-OS 6.
The following diagram shows a simplified structure of a Matter application which runs on the top of the Mbed-OS.
ARM Mbed-OS
Arm Mbed OS is an open source embedded operating system designed specifically for the “things” in the Internet of Things. It includes all the features you need to develop a connected product based on an Arm Cortex-M microcontroller, including security, connectivity, an RTOS and drivers for sensors and I/O devices.
Mbed OS provides an abstraction layer for the microcontrollers it runs on, so that developers can focus on writing C/C++ applications that call functionality available on a range of hardware. That means Mbed OS applications can be reused on any Mbed-compatible platform.
Mbed OS uses a hardware abstraction layer (HAL) to support the most common parts of a microcontroller, such as timers. This foundation facilitates writing applications against a common set of application programming interfaces (APIs); device automatically includes necessary libraries and driver support for standard MCU peripherals, such as I2C, serial and SPI.
Mbed OS has an RTOS core, so it supports deterministic, multithreaded, real-time software execution. The RTOS primitives are always available, allowing drivers and applications to rely on threads, semaphores, mutexes and other RTOS features.
The structure of Mbed OS enables matching applications and storage systems. In other words, where the block level storage options vary and are application dependent, The file system that best fits the IoT device can be chosen. The FAT file system - backed by an SD card - provides compatibility with other operating systems, such as Windows, Mac OS or Linux. When high reliability and recovery from power failure are important, it makes sense to use our embedded file system, backed with a (Q)SPI NOR flash chip.
Finally, Mbed OS implements the retargeting layer and boot process integration of each supported toolchain, so application development feels similar to C or C++ development for any other operating system.
Bluetooth and IP stacks
In the Mbed-oS platform applications, the Bluetooth LE interface is used to perform pairing and Wi-Fi network provisioning operations between the Matter device and the Matter controller. Afterwards, the fully provisioned device is able to communicate with other devices inside the Wi-Fi network.
For the Bluetooth LE communication purposes, the Mbed-OS platform application is using ARM Mbed BLE (also called BLE_API) - Bluetooth Low Energy software solution which interfaces with the BLE controller on the hardware target. Arm Mbed BLE hides the BLE stack’s complexity behind C++ abstractions and is compatible with all BLE-enabled Mbed board. The Mbed OS BLE_API automatically configuring the clocks, timers and other hardware peripherals to work at their lowest power consumption.
For Wi-FI communication purposes, the Mbed-OS application is using the internal Mbed LWIP stack and Mbed Socket API together. To integrate it with Matter network layer, special glue socket layer has been introduced to take care of adapting the Mbed socket to BSD interface which is used inside the Matter endpoints implementation.
Matter integration
The Bluetooth LE and Wi-Fi used stacks provided by the Mbed-OS have been integrated with the Matter stack using a special intermediate layer.
This layer contains platform-specific implementations of abstract manager interfaces defined in the Matter stack. The application is able to use Matter's platform agnostic interfaces and no additional platform-related actions are needed to perform communication through the Matter stack.
Matter example applications
Sample Matter applications are provided for the Mbed OS platform. They can be used to speed up development:
Example configuration
Each of the supporting examples contains the config.in file which allows you to configure the application in a proper way. You can define/disable/enable application settings. Then they are propagated through Mbed-OS and Matter stack build systems.
Matter stack configuration
In each of supported examples, the Matter stack can be configured by modifying CHIPProjectConfig.h file which is placed inside the project directory.
Mbed-OS configuration
Mbed-OS gives possibility to tweak its parameters by using the Mbed-OS configuration system. The same configuration system can be used to change default hardware target setup used in application. Additionally, it is the first place for adding support of the new hardware target support into the application. Mbed-OS configuration system can be accessed by modifying the mbed_app.json file which exists in each sample project directory.
Build system
The Mbed-OS platform makes use of the following build systems to generate ninja build scripts:
- GN - Used by the Matter project in majority of cases.
- CMake (+ mbed-tools) - Used by the Mbed-OS user application and other components within Mbed ecosystem.
Matter's stack and platform modules are built with GN and output a library file. The application, Mbed-OS and target specific libraries are built with CMake and the Matter library file is imported during the compilation process.
Build profiles
Arm Mbed OS defines three collections of toolchain flags used during the build:
- develop
- release
- debug
Build profiles can be easy selected when building example application using either vscode task or its associated build script directly (mbed_examples.sh).
For more details about each of this profiles, please visit official ARM Mbed documentation.